1. Field of the Invention
The present invention relates to a magnetic sensor, particularly to a high-sensitivity magnetic sensor used for a high-density magnetic recording/reading head.
2. Description of the Prior Art
It has been recently requested to further improve the recording density of an external memory such as a hard disk. Thereby, it is requested for a magnetic head for reading information from a recording medium to accurately detect a weaker external magnetic field.
The so-called MR device using metals or alloys has been used for a reading magnetic head.
However, a conventional MR device has problems that resistance change is too small for an external magnetic field and no sufficient output can be obtained from a weak external magnetic field. Therefore, the MR device cannot correspond to magnetic recording at a very-high recording density of, for example, 10Gb/in2 or more.
Therefore, to solve the above problems, a magnetic sensor for detecting a nonequilibrium spin injected into a paramagnetic metallic layer from a spin-polarized ferromagnetic material oxide is proposed (official gazette of Japanese Patent Application Laid-Open No. 9-214018).
The magnetic sensor disclosed in the official gazette of Japanese Patent Application Laid-Open No. 9-214018 is characterized by connecting a spin injection layer and a spin detection layer respectively made of an almost-completely-spin-polarized ferromagnetic material oxide each other by an intermediate layer made of a paramagnetic metal.
However, the above structure is troublesome because it is necessary to form a submicron-order narrow portion between the spin injection layer and the spin detection layer and moreover, accurately adjust the position of the intermediate layer having a size of micron m or shorter order to the narrow portion between the spin injection layer and spin detection layer.
Moreover, because there are restrictions on the working accuracy by photolithography and etching, it takes a lot of time and it is very difficult to accurately cut the narrow portion, accurately adjust the position of the intermediate layer, and decrease the planar dimension of the intermediate layer to less than micron order. Thereby, a trouble occurs that the production efficiency is extremely lowered.
Furthermore, when the planar dimension of the intermediate layer is several-micron order or more, spin-polarized carriers injected into the intermediate layer from the spin injection layer must move several microns or more in the intermediate layer as for the above structure.
Moreover, as for the above distance, a spin flip occurs during moving and information is lost. Therefore, the difference between the effective numbers of electrons in an up-spin band and a down-spin band decreases when the magnetization directions of the spin injection layer and the spin detection layer are not parallel each other and as a result, the above conventional example causes a trouble that an output voltage lowers.
Furthermore, the above conventional example has the following problem on the material.
That is, when the intermediate layer is made of a nonmagnetic single element such as Au or a nonmagnetic alloy such as Auxe2x80x94Ge, it is difficult to form a high-quality trilayer having less defects with an almost-completely-spin-polarized ferromagnetic metallic oxide such as (La,Sr)MnO3.
To form a superior film with an almost-completely-spin-polarized ferromagnetic metal, a high temperature of 600 degrees centigrade or above is necessary when using, for example, (La,Sr)MnO3. Thus, an intermediate layer made of a nonmagnetic element such as Au having a small adhesive strength with an oxide and a low melting point or a nonmagnetic alloy such as Auxe2x80x94Ge has a problem that the layer causes an interface reaction with (La,Sr)MnO3 or cohesion by itself, a reaction layer is consequently formed on an interface, or a grain boundary occurs on the intermediate layer or a spin detection layer (or spin injection layer) formed on the intermediate layer.
In the above case, when the intermediate layer cohesion like an island at a high temperature, it is impossible to uniformly hold the intermediate layer with an almost-completely-spin-polarized ferromagnetic oxide such as (La,Sr)MnO3 and thereby, separation or crack occurs on the interface between the intermediate layer and a spin injection layer (or spin detection layer).
When a trilayer is not high-quality, a reaction layer is present on the interface between an intermediate layer and a spin injection layer (or spin detection layer), or a grain boundary is present in the intermediate layer or spin injection layer (or spin detection layer), spin of carriers flips at the place, and the difference between the numbers of electrons of an up-spin band and a down-spin band effectively decreases in the intermediate layer and an output voltage lowers. This is not preferable for the performance of a device and simultaneously, a disadvantage occurs that the productivity of devices lowers.
Moreover, there is another problem that an output voltage lowers when an intermediate layer into which spin-polarized carriers are injected is made of a nonmagnetic single element such as Au or an alloy such as Auxe2x80x94Ge having a small resistivity.
This is because a nonmagnetic metal having a small resistivity such as Au has a large paramagnetic susceptibility and a large state density nearby a Fermi plane, the effective chemical potential difference between up-spin carrier and down-spin carrier due to nonequilibrium magnetization produced in an intermediate layer caused by the difference between the numbers of electrons in a up-spin band and a down-spin band decreases and an output voltage lowers. This is not preferable for the performance of a device.
It is an object of the present invention to provide a magnetic sensor having a device structure capable of improving the disadvantages of the above conventional example, particularly raising an output voltage, and improving the productivity.
A magnetic sensor of the present invention uses a basic structure in which a spin injection layer and a spin detection layer respectively made of an almost-completely-spin-polarized oxide ferromagnetic material are formed and a layer made of a nonmagnetic conductive oxide is held between the two layers as an intermediate layer.
In this case, the almost-completely(highly)-spin-polarized oxide ferromagnetic material constituting the spin injection layer and spin detection layer uses at least one of the perovskite-structure oxide Ln1xe2x88x92XAXMnO3 (Ln denotes at least one of the elements such as lanthanoid, Bi, and Y, A denotes at least one of alkali-earth metals and Pb, and X is set so as to meet the relation 0.15xe2x89xa6Xxe2x89xa60.5), pyrochlore-structure oxide (Tl1xe2x88x92XInX)2Mn2O7 (0xe2x89xa6Xxe2x89xa61), layered-perovskite-structure oxide (Ln1xe2x88x92XAX)n+1 MnnO3n+1 (Ln denotes at least one of the elements such as lanthanoid, Bi, and Y, A denotes at least one of alkali-earth metals and xe2x89xa6Pb, and the relations 0.15xe2x89xa6Xxe2x89xa60.7 and n=2.3 are set), spinel-structure oxide Fe3O4, and rutile-structure oxide CrO2.
Moreover, the nonmagnetic conductive oxide constituting the intermediate layer uses at least one of the perovskite-structure oxides SrMoO3, SrIrO3, La1xe2x88x92XAXRhO3 (Xxe2x89xa70.3), La-doped SrTiO3 (doping value of 0.1 wt % or more), and Nb-doped SrTiO3 (doping value of 0.05 wt % or more), and the rutile-structure oxides RuO2 and IrO2.
Furthermore, as described above, a magnetic sensor of the present invention has a structure in which the conductive intermediate layer (symbol 3 in FIG. 1) not easily reacting on an almost-completely-spin-polarized ferromagnetic metallic oxide and having a high lattice matching is held between two layers such as the spin injection layer (symbol 2 in FIG. 1) and the spin detection layer (symbol 4 in FIG. 1) respectively made of the ferromagnetic metallic oxide.
Therefore, the present invention provided with the above trilayer does not require the alignment necessary for the fabrication process of the prior art but it has an advantage that the plane size of an intermediate layer is only worked into submicron order through conventional photolithography and etching. Moreover, by using the above structure, spin-polarized carriers injected into an intermediate layer from a spin injection layer move in the film-thickness direction in the intermediate layer and therefore, it is possible to easily improve an output voltage only by decreasing the film thickness.
Moreover, a magnetic sensor of the present invention uses a nonmagnetic conductive oxide having a resistivity relatively larger than that of a single metal or alloy for an intermediate layer. Therefore, a large chemical potential difference is produced due to even a very small difference between the numbers of electrons of an up-spin band and a down-spin band in a paramagnetic metallic layer produced due to injection of spin-polarized carriers from a spin injection layer and consequently, a large output voltage can be obtained. Furthermore, because the intermediate layer uses a nonmagnetic conductive oxide not easily reacting with an almost-completely-spin-polarized ferromagnetic metal, no reactive layer is formed on the interface between the intermediate layer and the spin injection layer (or spin detection layer).
Furthermore, the intermediate layer of the present invention is closely lattice-matched to the spin injection layer and to the spin detection layer. Therefore, the intermediate layer and a spin injection layer (or spin detection layer) epitaxially grow and these layers do not form a grain boundary by being transformed into polycrystal.
Therefore, it is possible to prevent an output voltage from lowering due to the fact that spin of spin-polarized carriers flips on the interface or grain boundary between the spin injection layer (or spin detection layer) and the intermediate layer.
Furthermore, a nonmagnetic conductive oxide constituting an intermediate layer does not aggregate during the deposition of a trilayer because the oxide has a melting point higher than that of a single element such as Au or an alloy such as Auxe2x80x94Ge and a large adhesive strength with an almost-completely-spin-polarized ferromagnetic oxide such as (La,Sr)MnO3. Therefore, it is possible to solve the conventional problem that the productivity of devices is lowered because separation or crack occurs on the interface between an intermediate layer and a spin injection layer (or spin detection layer).